Known in the art is a material in which the dielectric layer contains kaolin and a triple copolymer of methacrylic acid with acrylic acid esters (cf. Katahiri K., Ishikawa S., et al., Electrostatic Recording Material and Method for the Production thereof, U.S. Pat. No. 4,268,595, 1981).
In another known material, the dielectric layer contains colloidal silicon dioxide and a copolymer of methacrylic acid with a methacrylate or acrylate (cf. Kitahara M., et al., Electrostatic Recording material Having a Dielectric Copolymer Coated Layer, U.S. Pat. No. 4,097,646, 1978). The presence of a pigment with a hydrophilic surface which retains considerable quantities of absorbed water in the compositions of the dielectric layer does not permit achieving a high charging capacity and charge retention over a certain time period.
This disadvantage may be eliminated by using as a pigment of the dielectric layer a a layer of a finely divided pyrogenic silicon dioxide with the surface alkylated or modified with organosilicon compounds such as dimethyldichlorosilane, its derivatives or polymethylcyclosiloxanes (cf. USSR Inventor's Certificates No. 1 35558, Off. Bull. No. 30, 1983; No. 1004951, Off. Bull. No. 10, 1983; No. 1011576, Off. Bull. No. 14, 1983; No. 1056125, Off. Bull. No. 43, 1983, respectively).
However, owing to the fact that the surface of the pyrogenic silicon dioxide exhibits weak acceptor properties, it has a destabilizing effect on the super molecular structure of the polymeric binders used during the layer formation thus limiting the values of the basic electrophysical characteristics of the material.
Known in the art are a number of materials which comprise titanium dioxides as a pigment and a binder in the form of a mixture of phenol formaldehyde resin and vinyl acetate (cf. Brown A.D., Heights C., Blumental J., Electrographic Record System Having a Self-Spacing Medium, U.S. Pat. No. 3,711,859, 1973), a copolymer of vinyl acetate and crotonic acid (cf., Funderbark K., Receiver Sheets for Electrostatic Recording, U.S. Pat. No. 3,861,954, 1975), a mixture of a copolymer of vinyl acetate with vinyl chloride and nitrocellulose (cf. Fujie S., Miyashima T., Electrically Sensitive Paper, Japanese Pat. No. 55-33995, 1980).
These materials have a charging capacity of up to 30 to 40 V/.mu.m, which provides for a high contrast of an image but which is insufficient for reproducing half-tones. This is due to the properties of titanium dioxide which is a semiconductor to a large extent rather than an insulator so that its bulk resistance is inadequate.
Known in the art is a material for the electrostatic data recording consisting of an electrically conducting support and a dielectric layer containing a mixed finely divided pyrogenic titanium and silicon dioxide with a titanium content between 10 and 50% by weight and a polymeric binder (cf. USSR Inventor's Certificate No. 1046736, Off. Bull. No. 37, 1983). The contents of the components in the layer in % by weight are as follows:
______________________________________ Mixed titanium and silicon oxide 17-75 Polymeric binder 25-83. ______________________________________
The surface of the mixed oxide may be modified with a polyalkylchlorosilane or its derivatives.
The dielectric layer of this material has a charging capacity of the order of 50 to 60 V/.mu.m so that it can be used for producing half-tone images of a moderate quality, but this charging capacity is inadequate for reproducing high-quality half-tone originals.
The charging capacity of this material is limited by the presence, on the surface of the mixed oxide used, of chemically active groups which are eventually the charge carriers. Modifying the surface of the mixed oxide with alkylchlorosilanes or their derivatives does not improve the charging capacity of the material even if such modification proved effective for pure silicon dioxide (cf. USSR Inventor's Certificate No. 1004951, No. 1011576).